The little-known Scottish fund manager who built the UK market's most successful investment strategy of recent years has been poached from Standard Life Investments to become chief executive at rival Aviva Investors.

Euan Munro, architect of Standard Life's global absolute return strategy (GARS) which has grown to a remarkable £25 billion in five years and helped drive Standard's share price, will spend six months on garden leave before taking up the job in London with a likely seven-figure package.

Mr Munro, 43, who joined Standard from Scottish Provident in 1995, chairs Standard Life Investments' Strategic Investment Group and is responsible for managing almost $200bn (£135bn) of client funds, Aviva noted.

After becoming global head of multi-asset investing and fixed income in 2008, he established and developed the flagship £18bn GARS fund which has returned 50% since launch and underpinned the broader success of SLI, itself a key element in Standard Life's strong performance. Mr Munro will report to Mark Wilson, the new chief executive charged with turning round Aviva, who said: "This is an important appointment for Aviva. Mr Munro was the outstanding candidate to lead Aviva Investors."

Keith Skeoch, the £4.3m-a-year chief executive of SLI, stressed his empire's "team culture" and said Guy Stern would join the SLI board as head of multi-asset and macro investing. "Guy's appointment reflects the strength of his leadership of our multi-asset investing team and his investment track record. Guy has been responsible for the day-to-day running of our multi-asset investments since 2008."

It is the second raid on the successful GARS team inside a year, coming after Invesco Perpetual lured David Millar, Dave Jubb and Richard Batty last September. Standard Life itself has only recently lost £2.5m a year finance director Jackie Hunt, hired by its other big UK rival Prudential to run its UK business.

Mr Skeoch said Mr Munro had "left to take up a broader senior business management role elsewhere" and thanked him for his contribution to the business.

Aviva's coup stunned the financial community. Harry Morgan, the former Edinburgh Fund Managers, Newton and Adam & Co private client manager who now runs Thomas Miller Investments' Edinburgh office, said: "Alongside the growth of Baillie Gifford, the growth of this fund has been the greatest fund management success for Edinburgh in the past 25 years, and it has happened under the radar."

Mr Munro said: "I am joining Aviva because I see a clear opportunity to unlock the potential of Aviva Investors, a well-established business with impressive scale and significant investment talent."

The London-based group has some £280bn under management compared with SLI's £170bn in Edinburgh. Observers said Mr Munro, married with three children, would be signing up for a substantial seven-figure package – his current boss Mr Skeoch earned a total £4.35m last year at the smaller SLI, including £3.9m in bonus and shares. Mr Munro's rewards at SLI "might have reached seven figures given the growth of the fund", one fund manager said.

He added: "It is disappointing to see a big hitter leaving Edinburgh. GARS has been an easy sell to the adviser community and they have done it brilliantly, but is the fund now too big and has done all it can do? It's possible that Euan Munro is doing the classic fund manager thing and leaving at the top."

SLI commented: "All our processes will remain in place. Our MAI strategies have consistently outperformed their targets since launch and we expect them to continue to meet their performance targets going forward."

Adrian Lowcock, investment chief at brokers Hargreaves Lansdown, said: "It is a big loss to Standard Life, but GARS has always been quite a broad team-based approach."

Darius McDermott, at brokers Chelsea Financial Services, said Mr Stern could "certainly take some of the credit" for GARS' success, and he would consult with the company before deciding whether to downgrade the fund to a "hold".